Cellular communications systems are well-known. Analog cellular systems such as designated AMPS, ETACS, NET-450, and NET-900 have been deployed successfully throughout the world. More recently, digital cellular systems such as designated IS-54B in North America and the pan-European GSM system have been introduced. These systems, and others, are described, for example, in the book titled Cellular Radio Systems by Balston, et al., published by Artech House, Norwood, Mass., 1993.
The IS-54B specification entitled Cellular System Dual-Mode Mobile Station Base Station Compatibility Standard (available from the Telecommunications Industry Association, 2001 Pennsylvania Avenue, N.W., Washington , D.C., 20006) provides increased system capacity through digital time division multiple access (TDMA) while allowing compatibility with existing analog systems. Mobile stations designed to meet the IS-54B specification are able to function with both the new TDMA systems and the existing AMPS analog systems. Throughout this specification the terms mobile station, cellular telephone, cellular phone, mobile phone, and cellular radiotelephone are used interchangeably to refer to the same device. One drawback to the current specification is that the both the digital and analog systems make use of the existing AMPS analog control channels. Therefore TDMA capable mobile stations are constrained by the old analog protocols and are not able to fully utilize all the features possible with digital communications.
Currently, cellular mobile radiotelephones are limited in stand-by battery life because they must continuously monitor the analog control channel for paging messages indicating an incoming call. Even with high capacity batteries, stand-by times in excess of about 24 hours are rare. This may be contrasted with paging receivers, or "beepers", which have battery lives of about 100-200 hours from a single AA battery achieved by cyclical operation. The need for longer battery life in cellular radiotelephones is therefore self-evident.
A digital control channel (DCC) has recently been proposed to the Telecommunications Industry Association (TIA). The DCC specification is identified as PN 3011-1 and PN 3011-2 and is available from the TIA at the above address. When adopted, the DCC will become part of a new IS-54C specification. The specifications PN 3011-1 and PN 3011-2 are incorporated herein by reference in their entirety.
One feature of the DCC is called short message service (SMS.) With SMS it will be possible to send alphanumeric messages to compatible mobile stations in a manner similar to that presently done with paging receivers. This feature opens the door for many new cellular phone options.
Unlike voice communications in which a caller is waiting for a response from the called-party, alphanumeric messages do not require an immediate response and can be stored and subsequently delivered to the mobile station some period of time after origination. This allows the mobile phone to adopt what will hereinafter be referred to as a "pager-only mode" of operation.
The pager-only mode of the mobile station will allow the user to receive SMS messages but not to receive incoming conversation type calls. The call origination capability remains thereby allowing the user to place calls without exiting the pager-only mode. The pager-only mode offers many advantages to the user not the least of which is the benefit of much longer battery life. The pager-only mode also functions as a do-not-disturb mode for business meetings, and allows the mobile station user to perform "call screening" of incoming calls. Unlike the known broadcast page receiver (i.e., "beeper") , the mobile phone is immediately available to place a call to the message originator.